TECHNICAL FIELD
[0001] The present invention particularly relates to a translucent hard thin film to be
formed on a surface of a substrate made of glass, etc. required to be transparent
and to have high film strength.
BACKGOUND ART
[0002] There is known a technique of forming an abrasion resistant film made of a mixture
of a silicon-type compound (Si
3N
4, SiC and SiO
2) on a surface of a substrate (metal, ceramic and plastic, etc.) (Patent Document
1).
RELATED ART DOCUMENTS
PATENT DOCUMENT
[0003] Patent Document 1: Japanese Patent Unexamined Patent Publication (Kokai) No.
S60-221562
SUMMARY OF THE DISCLOSED SUBJECT MATTER
[0004] However, the abrasion resistant film formed on the substrate surface in the patent
document 1 had low transmissivity and could not used for the purposes requiring transparency.
[0005] According to another aspect of the present invention, there is provided a translucent
hard thin film having high transmissivity and film strength.
[0006] According to the present invention, there is provided a translucent hard thin film
formed on a surface of a substrate, configured by a laminated film having a superlattice
structure, wherein a plurality of SiO
2 layers and SiC layers are stacked alternately, a film thickness per layer is 5nm
to 30nm in a SiO
2 layer and 30 to 60% of that of the SiO
2 layer in a SiC layer, and an entire film thickness thereof is 3000nm or more.
[0007] In the invention above, the SiC layer is preferably formed on a surface of the substrate
or already formed SiO
2 layer by a method below.
[0008] The method is a film forming method of a thin film, using a film formation apparatus
(radical assisted sputtering apparatus) having a configuration that a reaction processing
region and a plurality of film forming regions are arranged being spatially separated
from one another in a single vacuum container, each region can be controlled independently
and processing is performed on a moving substrate; wherein after performing sputtering
on any of a plurality of targets made of different materials in the respective film
formation processing regions in an inert gas atmosphere to form an interlayer thin
film containing silicon and carbon, the interlayer thin film is exposed to (or brought
to contact with) plasma generated under an atmosphere of a mixed gas of an inert gas
and hydrogen in the reaction processing region to obtain an ultrathin film by film
conversion, then, formation of the interlayer thin film and film conversion into the
ultrathin film are repeated to the ultrathin film.
[0009] According to the present invention, there is also provided an optical substrate,
wherein the translucent hard thin film of the present invention is formed on the substrate
made of glass. The optical substrate has properties that a wavelength is 650nm to
700nm, transmissivity is 70% or higher, Vickers hardness on the thin film side is
1500 or higher and a coefficient of dynamic friction is 0.5 or smaller.
[0010] Since a translucent hard thin film according to the present invention is configured
by a laminated film having a superlattice structure, wherein a SiO
2 layer and a SiC layer each having a specific film thickness are stacked alternately,
the transmissivity and film strength can be enhanced. Since the thin film according
to the present invention has high transmissivity and film strength, it is useful,
for example, as a window material of a sandblast apparatus, etc. and extremely useful
for other optical use purposes in which transmissivity and film strength are required.
BRIEF DESCRIPTION OF DRAWINGS
[0011]
[FIG. 1] FIG. 1 is a sectional view showing a configuration of a translucent hard
thin film according to the present invention.
[FIG. 2] FIG. 2 is a partial cross-sectional view showing an example of a film forming
apparatus for performing a RAS method.
[FIG. 3] FIG. 3 is a partial vertical sectional view along the line III-III in FIG.
2.
DESCRIPTION OF NUMERICAL NOTATIONS
[0012]
100... optical substrate, 102... laminated film (translucent hard thin film), 104...
SiO2 layer, 106... SiC layer, S... substrate,
1... film forming apparatus (sputtering apparatus), 11... vacuum container, 13...
substrate holder, 12, 14 and 16... partition wall
20 and 40... film formation process region, sputtering source (21a, 21b, 41a and 41b...
magnetron sputtering electrode, 23 and 43...AC source, 24 and 44... trans, 29a, 29b,
49a and 49b... target), sputtering gas supply means (26 and 46... sputtering gas cylinder,
25 and 45... mass flow controller),
60... reaction processing region, 80... plasma source (81... case body, 83... dielectric
plate, 85a and 85b... antenna, 87... matching box, 89... high frequency power source),
reaction processing gas supply means (68... reaction processing gas cylinder, 67...
mass flow controller)
EXEMPLARY MODE FOR CARRYING OUT THE DISLCOSED SUBJECT MATTER
[0013] As shown in FIG. 1, an optical substrate 100 of the present embodiment comprises
a substrate S for providing translucency and film strength, and a surface of the substrate
S is covered with a translucent hard laminated film 102.
[0014] As a material for composing the substrate S is, for example, crystal (crystal, lithium
niobate and sapphire, etc.), glass (BK7, quartz and low-melting-point glass) and plastic,
etc. may be mentioned. In the present embodiment, in particular, the effects of the
present invention is easily brought out when the substrate S is configured by a relatively
soft material, such as glass (6H to 7H) and plastic. Note that the number in brackets
is a value of pencil hardness measured by a method based on JIS-K5600-5-4.
[0015] A laminated film 102 as an example of the translucent hard thin film according to
the present invention has a superlattice structure, wherein a plurality of SiO
2 layers 104 and SiC layers 106 are stacked alternately, and the entire film thickness
is 5000nm or more and preferably 7000nm or more. When the entire film thickness is
5000nm or more, sufficient film strength can be given even when configuring the substrate
S with relatively soft material, such as glass. When configuring the substrate S with
a relatively hard material, such as sapphire, sufficient film strength can be obtained
even when forming the laminated film 102 to have an entire film thickness of as thin
as 2000nm or so. However, since a sapphire material is expensive, there have been
demands for giving sufficient film strength to the substrate S composed of a relatively
inexpensive material like glass.
[0016] Note that "superlattice structure" in this embodiment indicates the structure formed
by controlling film thicknesses of different materials on nano basis and stacking
the films.
[0017] In the present embodiment, film thicknesses of the layers 104 and 106 composing the
laminated layer 102 are as follows. The SiO
2 layer 104 is 5nm or thicker per layer, preferably 10 nm or thicker but not thicker
than 30nm, preferably not thicker than 25nm preferably not thicker than 20nm. When
the film thickness of the SiO
2 layer 104 is too thin, it is liable that the superlattice structure cannot be formed.
While when it is too thick, Vickers hardness could decline. A thickness per layer
of the SiC layer 106 is 30% or more of the film thickness of the SiO
2 layer 104, preferably 40% or more, more preferably 45% or more but not more than
60%, preferably not more than 55% and more preferably not more than 50%. The reason
why the film thickness of the SiC layer 106 is set in accordance with the film thickness
of the SiO
2 layer 104 is to keep the Vickers hardness of the thin film. When the film thickness
of the SiC layer 106 is too thin, it is liable that the superlattice structure cannot
be configured. While when it is too thick, the transmissivity is liable to be declined.
[0018] The number of layers 104 and 106 composing the laminated film 102 changes depending
on the total thickness of the laminated film 102 and film thicknesses of the layers
104 and 106. But it is preferable that, for example, when the total thickness of the
laminated film 102 is 7000nm, the film thickness of the SiO
2 layer 104 is 5 to 30nm or so, the thickness of the SiC 106 is 1.5 to 19nm or so,
the number of layers 104 and 106 is 300 to 800 or so, respectively, and they are alternately
and repeatedly stacked so as to form the laminated film 102.
[0019] The laminated film 102 of the present embodiment has high transmissivity and film
strength. Specifically, in a state where the laminated film 102 is provided on the
substrate S, the transmissivity at a wavelength of 650nm to 700nm is 70% or higher
and preferably 75% or higher, Vickers hardness HV on the thin film side is 1500 or
higher, preferably 1700 or higher and more preferably 1800 or higher. Also, a coefficient
of dynamic friction µk may be set to be 0.5 or smaller. An optical substrate 100,
wherein a laminated film 102 as above is formed on the substrate S, can be used, for
example, as a window material of a sandblast apparatus, etc.
[0020] Vickers hardness HV is one of indentation hardness used generally as a value indicating
hardness of an object. The measurement method is, by using as an indenter a diamond
equilateral pyramid having a facing angle of 136° against a surface of a material,
to measure a diagonal length of a square indent caused by pressing a sample with a
certain weight load. A surface area of the indent is obtained from the diagonal length,
and a value obtained by dividing the weight load by the surface area is the Vickers
hardness. The Vickers hardness is indicated only by a numerical number with no unit.
[0021] In the present embodiment, the layers 104 and 106 may be formed on the substrate
S, for example, by a radical assisted sputtering (RAS) method. Particularly, when
forming a SiC layer 106, by forming the film while introducing hydrogen to a film
forming atmosphere, sufficient transmissivity and film strength can be given to a
finally obtained multilayer film 102 as will be explained later on.
[0022] As shown in FIG. 2 and FIG. 3, a film forming apparatus 1 as an example capable of
performing a RAS method (hereinafter, simply referred to as abbreviated "sputtering
apparatus 1") comprises a vacuum container 11 having an approximate rectangular parallelepiped
hallow shape. A pipe 15a for exhaust is connected to the vacuum container 11 and the
pipe is connected to a vacuum pump 15 for vacuuming inside the container 11. The vacuum
pump 15 is configured, for example, by a rotary pump and turbo molecular pump (TMP),
etc. A substrate holder 13 is provided inside the vacuum container 11. The substrate
holder 13 is configured by a cylinder-shaped member for holding the substrate S, on
which a film is formed, on its outer circumferential surface inside the vacuum container
11. The substrate holder 13 in this embodiment is provided in the vacuum container
11, so that a rotation axis Z extending in the cylindrical direction is in the vertical
direction (Y direction) of the vacuum container 11. By driving the motor 17, the substrate
holder 13 rotates about the axis Z.
[0023] In the present embodiment, there are two sputtering sources and one plasma source
80 provided around the substrate holder 13 arranged inside the vacuum container 11.
[0024] In front of the respective sputtering sources, film forming regions 20 and 40 are
formed, respectively. The regions 20 and 40 are surrounded from four directions by
partition walls 12 and 14 respectively protruding from an inner wall surface of the
vacuum container 11 toward the substrate holder 13, so that an independent space can
be secured for each of the regions inside the vacuum container 11. In the same way,
a reaction processing region 60 is formed in front of the plasma source 80. The region
60 is also surrounded from four directions by partition walls 16 protruding from the
inner wall surface of the vacuum container 11 toward the substrate holder 13 and,
thereby, a space is also secured for the region 60 independently from the regions
20 and 40 inside the vacuum container 11. In the present embodiment, it is configured
that processing in each of the regions 20, 40 and 60 can be controlled separately.
[0025] The respective sputtering sources in the present embodiment are configured to be
a dual cathode type provided with two magnetron sputtering electrodes 21a and 21b
(or 41a and 41b). When forming a film (which will be explained later on), targets
29a and 29b (or 49a and 49b) are respectively held in a detachable way on surfaces
of one end of the electrodes 21a and 21b (or 41a and 41b). On the other end of the
electrodes 21a and 21b (or 41a and 41b), an AC source 23 (or 43) as a power supply
means is connected via a trans 24 (or 44) as a power control means for adjusting the
electric energy, so that it is configured to apply an alternating voltage of, for
example, 1k to 100kHz or so to the respective electrodes 21a and 21b (or 41a and 41b).
[0026] Each of the sputtering sources is connected to a sputtering gas supply means. The
sputtering gas supply means of the present embodiment comprises a gas cylinder 26
(or 46) for storing a sputtering gas and a mass flow controller 25 (or 45) for adjusting
a flow amount of the sputtering gas supplied from the cylinder 26 (or 46). The sputtering
gas is introduced to the region 20 (or 40) through a pipe. The mass flow controller
25 (or 45) is a device for adjusting a flow amount of the sputtering gas. After a
flow amount from the cylinder 26 (or 46) is adjusted by the mass flow controller 25
(or 45), the sputtering gas is introduced to the region 20 (or 40).
[0027] The plasma source 80 of the present embodiment comprises a case body 81 fixed to
cover an opening formed on the wall surface of the vacuum container 11 and a dielectric
plate 83 fixed to the case body 81. It is configured that, as a result that the dielectric
plate 83 is fixed to the case body 81, an antenna housing chamber is formed in a region
surrounded by the case body 81 and the dielectric plate 83. The antenna housing chamber
is connected with the vacuum pump 15 through a pipe 15a and the antenna housing chamber
can be in a vacuum state by exhausting by vacuuming using the vacuum pump 15.
[0028] The plasma source 80 comprises antennas 85a and 85b in addition to the case body
81 and the dielectric plate 83. The antennas 85a and 85b are connected to a high frequency
power source 89 via a matching box 87 for housing a matching circuit. The antennas
85a and 85b are supplied with power from the high frequency power source 89 and generate
an induction field inside the vacuum container 11 (region 60), so that plasma is generated
in the region 60. In the present embodiment, it is configured that an alternating
voltage having a frequency of 1 to 27MHz is applied from the high frequency power
source 89 to the antennas 85a and 85b to generate in the region 60 plasma of reaction
processing gas. A variable capacitor is provided in the matching box 87, so that the
power supplied from the high frequency power source 89 to the antennas 85a and 85b
can be changed.
[0029] The plasma source 80 is connected to a reaction processing gas supply means. The
reaction processing gas supply means in the present embodiment comprises a gas cylinder
68 for storing a reaction processing gas and a mass flow controller 67 for adjusting
a flow amount of the reaction processing gas to be supplied from the cylinder 68.
The reaction processing gas is introduced to the region 60 through a pipe. The mass
flow controller 67 is a device for adjusting a flow amount of the reaction processing
gas. After a flow amount from the cylinder 68 is adjusted by the mass flow controller
67, the reaction processing gas is introduced to the region 60.
[0030] Note that the reaction processing gas supply means is not limited to the configuration
above (namely, the configuration comprising one cylinder and one mass flow controller)
and may be configured to comprise a plurality of cylinders and mass flow controllers
(for example, as in a later explained embodiment, the configuration comprising three
gas cylinders separately storing an inert gas, oxygen and hydrogen and three mass
flow controllers for adjusting flow amounts of gases supplied from the respective
cylinder).
[0031] Next, an example of a film forming method of a multilayer film using the sputtering
apparatus 1 will be explained.
[0032] (1) First, preliminary preparation of film forming is made. Specifically, targets
29a and 29b (or 49a and 49b) are set on electrodes 21a and 21b (or 41a and 41b). Along
therewith, substrates S as film forming objects are set on the substrate holder 13
outside of the vacuum container 11 and housed in a load lock chamber in the vacuum
container 11.
[0033] On the outer circumferential surface of the substrate holder 13, a plurality of substrate
S are arranged discontinuously along the rotation direction (crossing direction) of
the substrate holder 13, and a plurality of substrates S are arranged discontinuously
along the parallel direction (vertical direction, Y direction) with the axis Z of
the substrate holder 13.
[0034] The targets 29a and 29b (or 49a and 49b) are obtained by shaping a film material
into a plate and held respectively on the surfaces of the electrodes 21a and 21b (or
41a and 41b), so that their longitudinal direction becomes parallel with the rotation
axis Z of the substrate holder 13 and their surfaces in the parallel direction face
the side surface of the substrate holder 13. In the present embodiment, those composed
of silicon (Si) are used as the targets 29a and 29b and those composed of carbon (C)
are used as the targets 49a and 49b.
[0035] As the target 49a and 49b, instead of those composed of carbon (C), those composed
of silicon carbide (SiC) which is a compound of a plurality of elements may be used
in some cases. As a silicon carbide target, those obtained, for example, by the method
below may be used. First, a silicon carbide powder is added with a dispersant, a binder
(for example, an organic binder) and water, agitated to fabricate a SiC slurry and
molded (for example, by casting molding, press molding and extrusion molding, etc.)
into a mold. Next, the obtained mold is fired, for example, in vacuum or in a non-oxidizing
atmosphere at 1450 to 2300°C or so (preferably 1500 to 2200°C and more preferably
1600 to 1800°C) to be sintered. Then, the obtained sintered body is impregnated with
melt Si in vacuum or in a reduced non-oxidizing atmosphere at 1450 to 2200°C or so
(preferably 1500 to 2200°C and more preferably 1500 to 1800°C) to fill pores in the
sintered body with Si. In the present embodiment, a SiC target having a density of
3g/cm
3 or higher obtained thereby may be used. With a uniform SiC target having a high density,
stable high-input discharge can be performed when forming a film by sputtering, which
can contribute to an improvement of the film forming rate.
[0036] Next, after moving the substrate holder 13 to the film forming chamber of the vacuum
container 11, the vacuum container 11 is tightly closed in a state where a door to
the load lock chamber is closed, and inside the vacuum container 11 is brought to
be in a high vacuum state of 10
-5 to 0.1Pa or so by using the vacuum pump 15. During this time, a valve is open and
the antenna housing chamber of the plasma source 80 is exhausted at the same time.
[0037] Next, the motor 17 starts to drive and rotates the substrate holder 13 about the
axis Z. Consequently, the substrates S held on the outer circumferential surface of
the substrate holder 13 revolve about the axis Z as a rotational axis of the substrate
holder 13 and move repeatedly among positions of facing to the regions 20 and 40 and
a position of facing to the region 60. In the present embodiment, sufficient rotation
rate of the substrate holder 13 is 10rpm or higher, but it is preferably 50rpm or
higher and more preferably 80rpm or higher. In the present embodiment, the upper limit
of the rotation rate of the substrate holder 13 is, for example, 150rpm or so and
preferably 100rpm.
[0038] (2) Then, film forming starts. When forming a SiO
2 layer 104 (a thin film made of silicon oxide), sputtering processing performed in
the region 20 and plasma exposure processing performed in the region 60 are repeated
sequentially. In that case, an interlayer thin film is formed on a surface of a substrate
S or an already formed SiC layer 106 in the sputtering processing in the region 20
and, after that, the interlayer film is subjected to film conversion and becomes an
ultrathin film in the plasma exposure processing in the region 60. As a result of
repeating the sputtering processing and plasma exposure processing, next ultrathin
film is deposited on an ultrathin film. This operation is repeated until the SiO
2 film 104 finally reaches a predetermined film thickness. Note that "interlayer thin
film" here is a thin film formed by passing through the region 20.
[0039] When forming a SiC layer 106 (a thin film made of silicon carbide), processing at
the region 40 also starts and successive sputtering processing performed at two regions
20 and 40 and the plasma exposure processing at the region 60 are repeated sequentially.
In that case, an interlayer thin film is formed on the substrate S or on a surface
of an already formed SiO
2 layer 104 by the both successive sputtering processing in the regions 20 and 40,
and the interlayer thin film becomes an ultrathin film by film conversion in the subsequent
plasma exposure processing in the region 60. As a result that the both sputtering
processing and the plasma exposure processing are performed repeatedly, next ultrathin
film is deposited on an ultrathin film. This operation is repeated until the SiC layer
106 finally reaches a predetermined film thickness. Note that "interlayer thin film"
here is a thin film formed by passing through both of the region 20 and the region
40.
[0040] In the present embodiment, because a plurality of the ultrathin films are deposited
to form the final thin film (a thin film having an intended film thickness), the term
"ultrathin film" is used for preventing confusing it with the finally obtained "thin
film" and also used in a meaning that it is well thinner than the final "thin film".
[0041] (3) In the present embodiment, as a result that film formation of a SiO
2 layer 104 and film formation of a SiC layer 106, which will be explained below, are
repeated for necessary times, the substrate S is covered with a multilayer film 102
having a cyclic structure composed of SiO
2 layers 104 and SiC layers 106.
< Film Formation of SiO2 Layer 104 >
[0042] After confirming pressure stability inside the vacuum container 11, a pressure in
the region 20 is adjusted, for example, to 0.05 to 0.2Pa, then, a predetermined flow
amount of sputtering gas is introduced to the region 20 from the gas cylinder 26 via
the mass flow controller 25.
[0043] In the present embodiment, an inert gas was used alone as a sputtering gas, and a
reaction gas, such as nitrogen and oxygen, is not used together. Therefore, the film
forming rate does not decline comparing with that in the case of a reactive sputtering
method wherein a reaction gas as such is introduced together. An introducing flow
amount of an inert gas is a little larger than that in the usual condition, such as,
100 to 600sccm, preferably, 400 to 550sccm or so. Consequently, it becomes an inert
gas atmosphere around the targets 29a and 29b. In this state, an alternating voltage
is applied to the electrodes 21a and 21b from the AC source 23 via the trans 22 so
as to cover the targets 29a and 29b with an alternating electric field. By introducing
a little larger amount than that in the normal condition (for example, 150sccm or
so), various properties of respective films (adhesiveness, film stress and mechanical
characteristics, etc.) are expected to be improved, consequently, it can contribute
to an improvement of film strength of the finally obtained multilayer film 102.
[0044] In the present embodiment, a power (sputtering power) is supplied, so that a sputtering
power density to the targets 29a and 29b becomes preferably 7.0W/cm
2 or higher and more preferably 8.0W/cm
2 or higher, but preferably 10.0W/cm
2 or lower and more preferably 9.0W/cm
2 or lower. "Power density" means a power (W) supplied to the targets 29a and 29b (or
49a and 49b) per unit area (cm
2) (It will be the same below).
[0045] By supplying power to the targets 29a and 29b, the target 29a becomes cathode (negative
electrode) at one point and the target 29b inevitably becomes anode (positive electrode)
at the same time. At the next moment, when the direction of the alternating power
changes, the target 29b in turn becomes cathode (negative electrode) and the target
29a becomes anode (positive electrode). As a result that the targets 29a and 29b in
a pair alternately become anode and cathode, a part of the sputtering gas (inert gas)
around the targets 29a and 29b emits electrons and becomes ionized. A leakage magnetic
field is formed on the surfaces of the targets 29a and 29b by magnets arranged at
the electrodes 21a and 21b, therefore, the electrons go around drawing a toroidal
curve in the magnetic field generated near the surfaces of the targets 29a and 29b.
Strong plasma is generated along the orbit of the electrons, ions of the sputtering
gas in the plasma are accelerated toward a target in a negative potential state (cathode
side) to collide with each of the targets 29a and 29b, so that atoms and particles
(Si atoms and Si particles) on the surfaces of the targets 29a and 29b are beaten
out (sputtered). These atoms and particles are film raw materials, materials for a
thin film, which adhere to the surface of the substrate S or already formed SiC layer
106 so as to form an interlayer thin film. Sputtering of a silicon target in the region
20 is as above.
[0046] In the present embodiment, the region 60 is activated together with activation of
the region 20. Specifically, a reaction processing gas in a predetermined flow amount
is introduced from the gas cylinder 68 to the region 60 via the mass flow controller
67 so as to bring the vicinity of the antennas 85a and 85b a predetermined gas atmosphere.
[0047] A pressure of the region 60 is maintained, for example, to 0.07 to 1Pa. Also, at
least during plasma is generated in the region 60, the pressure inside the antenna
housing chamber is maintained to 0.001Pa or lower. In a state where the reaction processing
gas is introduced from the cylinder 68, when a voltage having a frequency of 100k
to 50MHz (preferably 1M to 27MHz) is applied to the antennas 85a and 85b from the
high frequency power source 89, plasma is generated in a region facing to the antennas
85a and 85b in the region 60. Power (plasma processing power) supplied from the high
frequency power source 89 may be as large as, for example, 3kW or more, preferably
4kW or more and more preferably 4.5kW or more when the substrate S is configured by
a glass material while as small as, for example, 1kW or less, preferably 0.8kW or
less and more preferably 0.5kW or less.
[0048] When forming a SiO
2 layer 104, oxygen is used as a reaction processing gas. Thus, plasma of an oxygen
gas to be generated is introduced to the region 60. When the substrate holder 13 rotates
to feed substrates S to the region 60, an interlayer thin film formed on a surface
of each substrate S or already formed SiC layer 106 is subjected to plasma exposure
processing in the region 20 and, thereby, converted to an incomplete silicon oxide
having a desired composition (SiO
x2 (x1<x2<2)) or silicon oxide (SiO
2) so as to form an ultrathin film. Plasma exposure performed on an interlayer thin
film in the region 60 is as explained above.
[0049] In the present embodiment, until an ultrathin film to be formed on a surface of the
substrate S or already formed SiC layer 106 reaches a predetermined film thickness,
the sputtering and plasma exposure are repeated so as to generate a thin film (SiO
2 layer 104) composed of a silicon oxide having a desired film thickness.
< Film Formation of SiC Layer 106 >
[0050] After confirming pressure stability inside the vacuum container 11 as same as when
forming a SiO
2 film 104, a pressure in the region 20 is adjusted, for example, to 0.05 to 0.2Pa,
then, a predetermined flow amount of sputtering gas is introduced from the gas cylinder
26 to the region 20 via the mass flow controller 25.
[0051] An inert gas is used alone as a sputtering gas. An introducing flow amount of the
inert gas is, for example, 100 to 600sccm and preferably 150 to 500sccm or so. After
bringing the vicinity of the targets 29a and 29b to be an inert gas atmosphere, an
alternating voltage is applied from the AC source 23 to the electrodes 21a and 21b
via a trans 22 so as to cover the targets 29a and 29b with an alternating electric
field.
[0052] In the present embodiment, sputtering power is supplied to the target 29a and 29b,
so that a sputtering power density becomes 1.2W/cm
2 or higher, preferably 1.4W/cm
2 or higher and particularly 1.5W/cm
2 or higher, but 5.0W/cm
2 or lower, preferably 3.5W/cm
2 or lower and particularly preferably 3.0W/cm
2 or lower.
[0053] As a result of supplying power to the targets 29a and 29b, the targets 29a and 29b
in a pair alternately become anode and cathode as explained above. Thereby, a part
of the sputtering gas (inter gas) in the vicinity of the targets 29a and 29b emits
electrons and becomes ionized. The emitted electrons go around drawing a toroidal
curve in the leakage magnetic field generated near the surfaces of the targets 29a
and 29b. Strong plasma is generated along the electron orbit and ions of the sputtering
gas in the plasma are accelerated toward a target in a negative potential state (cathode
side) to collide with each of the targets 29a and 29b, so that atoms and particles
on the surfaces of the targets 29a and 29b (Si atoms and Si particles) are beaten
out (sputtered). The atoms and particles are film raw materials, materials of a thin
film, which adhered to the surface of the substrate S or already formed SiO
2 layer 104. Sputtering of a silicon target in the region 20 is as above.
[0054] When forming a SiC layer 106, being different from the case of forming a SiO
2 layer 104 explained above, the region 40 is also activated together with activation
of the region 20 (supply of a sputtering gas and supply of power from the AC source
23). Specifically, a pressure in the region 40 is adjusted, for example, to 0.05 to
0.2Pa, then, a sputtering gas in a predetermined flow amount is introduced to the
region 40 from the gas cylinder 46 via the mass flow controller 46.
[0055] In the present embodiment, an inter gas was used alone as a sputtering gas in the
same way as above, and an introducing flow amount of the inter gas is, for example,
100 to 600sccm and preferably 150 to 500sccm or so. Thereby, the vicinity of the targets
49a and 49b also becomes an inert gas atmosphere. In this state, an alternating voltage
is applied from the AC source to the electrodes 41a and 41b via the trans 42 so as
to cover the targets 49a and 49b with an alternating electric field.
[0056] In the present embodiment, it is preferable to supply power to the targets 49a and
49b, so that a sputtering power density becomes predetermined times (for example,
2 to 5 times, preferably 2.3 to 4.5 times and particularly preferably 2.5 to 4 times
or so) a power density of sputtering the targets 29a and 29b. Thereby, it becomes
possible to efficiently form a thin film (SiC layer 106) composed of silicon carbide
having high transmissivity and film strength. As a result, transmissivity and film
strength of the finally formed laminated film 102 are also improved. The power density
to the targets 49a and 49b is, for example, 3.0 to 10.0W/cm
2, preferably 3.5 to 9.0W/cm
2 and particularly preferably 4.0 to 8.0W/cm
2 or so when the power density to the targets 29a and 29b above is 1.5 to 2.0W/cm
2.
[0057] Note that those composed of silicon (Si) may be used as the targets 29a and 29b and
those composed of silicon carbide (SiC) may be used as the targets 49a and 49b. In
that case, power can be supplied to the targets 49a and 49b, so that a sputtering
power density becomes predetermined times (for example, 2 to 3 times, preferably 2.3
to 2.8 times and particularly preferably around 2.5 times) a power density of sputtering
the targets 29a and 29b. In that case, when the power density to the targets 29a and
29b above is 3.0 to 4.0W/cm
2 (preferably 3.3 to 3.7W/cm
2 and particularly preferably around 3.5W/cm
2), the power density to the targets 49a and 49b may be, for example, 7.5 to 10W/cm
2, preferably 8.2 to 9.3W/cm
2 and particularly preferably around 8.8W/cm
2.
[0058] In the same way as explained above, by supplying power to the targets 49a and 49b,
the target 49a becomes cathode at one point and the target 49b inevitably becomes
anode at the same time. When the direction of the alternating power changes at the
next moment, the target 49b becomes cathode and the target 49a becomes anode. As a
result that the targets 49a and 49b in a pair alternately become anode and cathode,
a part of the sputtering gas (inert gas) around the targets 49a and 49b emits electrons
and becomes ionized. Since a leakage magnetic field is formed on the surface of the
targets 49a and 49b by magnets arranged at the electrodes 41a and 41b, the electrons
go around drawing a toroidal curve in the magnetic field generated near the surface
of the targets 49a and 49b. Strong plasma is generated along the orbit of the electrons,
ions of the sputtering gas in the plasma are accelerated toward a target in a negative
potential state (cathode side) to collide with each of the targets 49a and 49b, so
that atoms and particles (C atoms and C particles) on the surfaces of the targets
49a and 49b are beaten out. These atoms and particles are film raw materials, materials
for a thin film, which adhere to Si atoms and Si particles already adhered to the
substrate S or already formed SiO
2 layer 104 in this embodiment so as to form an interlayer thin film. Sputtering of
carbon targets (or silicon carbide target) in the region 40 is as above. Note that
the interlayer thin film here is composed of a mixture of elements (Si atoms or Si
particles and C atoms or C particles) and assumed not in a firm chemical binding state.
[0059] In the present embodiment, the region 60 is also activated together with activation
of the regions 20 and 40 in the same way as in the case of forming the SiO
2 layer 104 above.
[0060] When forming a SiC layer 106, it is preferable to use a mixed gas of an inert gas
and hydrogen as a reaction processing gas thereof. Then, ions (H
2+) of hydrogen molecules (H
2) and/or active species of hydrogen are present as a consequence, and they are introduced
to the region 60. When the substrate holder 13 rotates to feed the substrates S to
the region 60, an interlayer thin film composed of a mixture of Si and C formed on
the surface of each substrate S or already formed SiO
2 layer 104 in the regions 20 and 40 is subjected to plasma exposure processing and
turned to a compound of Si and C in a chemically firm binding state by film conversion
so as to form an ultrathin film. Plasma exposure to the interlayer thin film in the
region 60 is as explained above.
[0061] In the present embodiment, the both sputtering and the plasma exposure processing
are repeated until the ultrathin film to be formed on the surface of each substrate
or already formed SiO
2 layer 104 becomes a predetermined film thickness so as to form a thin film composed
of silicon carbide (SiC layer 106) having an intended film thickness.
[0062] The present inventors found the fact that, by bringing plasma generated in an atmosphere
of a mixed gas of an inert gas and hydrogen contact with the interlayer thin film
to convert it to an ultrathin film and, then, stacking ultrathin films to a predetermined
film thickness, a thin film composed of silicon carbide having high transmissivity
and film strength can be formed, consequently, it is possible to contribute to an
improvement of transmissivity and film strength of the finally obtained laminated
film 102. It is not all clear the reason why a thin film composed of silicon carbide
having excellent film properties can be obtained by performing processing as above
and that consequently contributes to an improvement of transmissivity and film strength
of the finally obtained laminated film 102. When forming a thin film composed of silicon
carbide, the configuration is largely different from that of normal continuous film
forming (vacuum deposition method, etc.) on the point that deposition of interlayer
thin film and exposure to plasma are independent in terms of time and cyclically repeated.
Furthermore, in the present embodiment, the deposited interlayer thin film is exposed
to particular plasma generated in an atmosphere of a mixed gas obtained by including
hydrogen in an inert gas. It is presumed that, by bringing particular plasma contact
with an interlayer thin film, during film conversion of the interlayer thin film into
an ultrathin film, the interlayer thin film efficiently takes in energy from ions
(H
2+) of hydrogen molecules and active species in plasma, consequently, highly strong
binding is attained between atoms, and transmissivity and film strength of a thin
film composed of silicon carbide are improved, which contribute to an improvement
of transmissivity and film strength of a finally laminated film 102 as a consequence.
The present inventors consider that particularly ions (H
2+) of hydrogen molecules in plasma work to promote binding of atoms in the interlayer
thin film.
[0063] A mixing ratio of an inert gas and hydrogen when forming a SiC layer 106 is preferably
97:3 to 80:20 (namely, a hydrogen concentration of 3 to 20%), more preferably 97:3
to 90:10 (hydrogen concentration of 3 to 10%), furthermore preferably 97:3 to 94:6
(hydrogen concentration of 3 to 6%) and particularly preferably around 95:5 (hydrogen
concentration of around 5%) in a volume conversion. There is a tendency that transmissivity
of a thin film composed of silicon carbide becomes higher as the hydrogen concentration
becomes higher, however, when the concentration is too high (for example, exceeding
20%), it may affect safety control in the manufacture procedure and it is liable that
balance becomes poor between transmissivity and film strength of a thin film composed
of silicon carbide to be formed, which may adversely affect a finally obtained laminated
film 102. On the other hand, when the hydrogen concentration is too low, transmissivity
of an obtained thin film composed of silicon carbide is deteriorated, which may adversely
affect the finally obtained laminated film 102 in the same way.
[0064] A flow amount of introducing the mixed gas when forming a SiC layer 106 is, for example,
300 to 1000sccm and preferably 400 to 600sccm or so. When the introducing flow amount
is small, it is liable that transmissivity and film strength of a silicon carbide
to be formed decline. While when the introducing flow amount is too large, a security
hazard may arise.
[0065] For example, argon and helium, etc. are possible as an inert gas in general in the
both sputtering processing and the plasma exposure processing explained above. In
the present embodiment, the case of using argon as an inert gas will be explained.
[0066] The embodiments explained above are described to facilitate understanding of the
present invention and are not to limit the present invention. Accordingly, respective
elements disclosed in the above embodiments include all design modifications and equivalents
belonging to the technical scope of the present invention.
[0067] In the above embodiments, the explanation was made on the case of forming a laminated
film 102 by using a sputtering apparatus 1 capable of performing a radical assisted
sputtering method, wherein magnetron sputtering as an example of sputtering is performed.
However it is not limited to this case and the film may be formed by other sputtering
methods using a film formation apparatus for other well known sputtering, such as
double-pole sputtering not using magnetron discharge. Note that the atmosphere in
the sputtering is an inert gas atmosphere in all cases.
EXAMPLES
[0068] Next, the present invention will be explained further in detail by using more specific
examples of the embodiments of the invention explained above.
< Experimental Examples 1 to 23 >
[0069] By using the sputtering apparatus 1 shown in FIG. 2 and FIG. 3, a plurality of glass
substrates BK7 as substrates S (note that a sapphire substrate was used in the example
1-1) were set on the substrate holder 13 and film formation of SiO
2 layer 104 and film formation of SiC layer 106 were repeated alternately under the
condition below, so that samples were obtained for respective examples, wherein a
laminated film 102 having a superlattice structure was formed on each substrate S.
Note that a SiO
2 layer 104 was formed as the first and last layers of the laminated film 102 in all
samples.
[0070] < Film Formation of SiO
2 Layer 104 >
* Film Forming Rate: 0.4nm/sec
* Substrate Temperature: room temperature
[0071] « Sputtering in Region 20 »
* Sputtering Gas: Ar
* Sputtering Gas pressure: 0.1Pa
* Flow Amount of Introducing Sputtering Gas: 500sccm
* Targets 29a and 29b: Silicon (Si)
* Sputtering Power Density: 8.5W/cm2
* Frequency of Alternating Voltage Applied to Electrodes 21a and 21b: 40kHz
[0072] << Plasma Exposure in Region 60 >>
* Reaction Processing Gas: O2
* Flow Amount of Introducing Reaction Processing Gas: 200sccm
* Power Supplied from High Frequency Power Source 89 to Antennas 85a and 85b (Plasma
Processing Power): 2kW
* Frequency of Alternating Voltage Applied to Antennas 85a and 85b: 13.56MHz
[0073] << Other >>
* Film Thickness per Layer: 4nm to 35nm (refer to Table 1)
* Number of Laminated Layers: 100 to 1120 layers (refer to Table 1)
[0074] < Film Formation of SiC Layer 106 >
* Film Forming Rate: 0.09nm/sec.
* Substrate Temperature: room temperature
[0075] << Sputtering in Region 20 >>
* Sputtering Gas: Ar
* Sputtering Gas Pressure: 0.1Pa
* Flow Amount of Introducing Sputtering Gas: 150sccm
* Targets 29a and 29b: Silicon (Si)
* Sputtering Power Density: 1.5W/cm2
* Frequency of Alternating Voltage Applied to Electrodes 21a and 21b: 40kHz
[0076] << Sputtering in Region 40 >>
* Sputtering Gas: Ar
* Sputtering Gas Pressure: 0.1Pa
* Flow Amount of Introducing Sputtering Gas: 150sccm
* Targets 49a and 49b: Carbon (C)
* Sputtering Power Density: 4.3W/cm2
(equivalent to approximately 2.9 times a power density for sputtering targets 29a
and 29b composed of silicon (Si))
* Frequency of Alternating Voltage Applied to Electrodes 41a and 41b: 40kHz
[0077] << Plasma Exposure in Region 60 >>
* Reaction Processing Gas: Ar + H2
* Hydrogen Concentration in Reaction Processing Gas: refer to Table 1
* Reaction Processing Gas Pressure: 0.3Pa
* Flow Amount of Introducing Reaction Processing Gas: 500sccm
* Plasma Processing Power: 2kW
* Frequency of Alternating Voltage Applied to Antennas 85a and 85b: 13.56MHz
[0078] << Other >>
* Film Thickness per Layer: 1.25nm to 21nm (refer to Table 1)
* Number of Laminated Layers: 100 to 1120 layers (refer to Table 1)
[0079] < Laminated Film 102 >
* Film Thickness: 2000nm to 7000nm (refer to Table 1)
<< Evaluation >>
[0080] Properties of the obtained samples were evaluated in the methods explained below,
and the results are shown in Tables below.
(1) Evaluation of Film Strength
[0081] A microhardness tester (MMT-X7 made by Matsuzawa Co., Ltd.) was used to measure hardness
of a laminated film surface of the example samples under the measurement condition
below.
* Indenter Shape: Vickers indenter (a=136°)
* Measurement Environment: temperature 20°C, relative humidity 60%
* Test Load: 25gf
* Loading speed: 10µ/s
* Maximum Load Creep Time: 15 seconds
(2) Evaluation of Transmissivity
[0082] Transmissivity at a wavelength of 650nm to 700nm was measured by using a spectral
photometer (product name: U-4000 made by Hitachi High-Technologies Corporation).
(3) Evaluation of Sliding Property
[0083] An automatic friction abrasion analyzer (Triboster TS501 made by Kyowa Interface
Science Co., Ltd.) using a horizontal linear reciprocating motion system was used
to measure a coefficient of dynamic friction (µk) on the laminated film side of the
samples under the condition of a load: 50g, speed: 60mm/min. and measurement reciprocating
times: 10 times.
[Table 1]
Experim ental Example |
Substrate |
Laminated Film |
SiO2 Layer |
SiC Layer |
Vicker's Hardiness |
Transmissivity |
Dynamic Friction Coefficient |
Material |
Film Thickness (nm) |
Film Thickness / Layer (nm) |
Number of Layer |
Film Thickness / Layer |
% to SiO2 |
Number of Layer |
Hydrogen Concentration (%) |
HV |
(%) |
µk |
*1 |
BK7 |
2000 |
15 |
100 |
5 |
33 |
100 |
5 |
1200 |
50 |
0.70 |
2 |
3000 |
150 |
150 |
1500 |
78 |
0.17 |
3 |
4000 |
200 |
200 |
1600 |
77 |
0.17 |
4 |
5000 |
250 |
250 |
1700 |
76 |
0.17 |
5 |
7000 |
350 |
350 |
1700 |
77 |
0.17 |
*6 |
7000 |
5 |
1120 |
1.25 |
25 |
1120 |
1300 |
80 |
0.40 |
7 |
1077 |
1.5 |
33 |
1077 |
1500 |
77 |
0.20 |
8 |
1000 |
2 |
40 |
1000 |
1800 |
75 |
0.17 |
*9 |
843 |
3.3 |
65 |
843 |
1800 |
50 |
0.17 |
*10 |
4 |
1094 |
2.4 |
60 |
1094 |
1800 |
55 |
0.17 |
*11 |
15 |
373 |
3.75 |
25 |
373 |
1400 |
80 |
0.30 |
12 |
359 |
4.5 |
33 |
359 |
1500 |
77 |
0.20 |
13 |
333 |
6 |
40 |
333 |
1700 |
75 |
0.17 |
*14 |
282 |
9.8 |
65 |
282 |
1800 |
50 |
0.17 |
*15 |
30 |
187 |
7.5 |
25 |
187 |
1300 |
80 |
0.50 |
16 |
175 |
10 |
33 |
175 |
1500 |
77 |
0.45 |
17 |
167 |
12 |
40 |
167 |
1500 |
75 |
0.40 |
*18 |
141 |
19.5 |
65 |
141 |
1800 |
50 |
0.17 |
*19 |
35 |
125 |
21 |
60 |
125 |
1800 |
55 |
0.17 |
"*" indicates a comparative example. |
[Table 2]
Experim ental Example |
Substrate |
Laminated Film |
Si02 Layer |
SiC Layer |
Vickers Hardness |
Transmissivity |
Dynamic Friction Coefficient |
Material |
Film Thickness (nm) |
Film Thickness / Layer (nm) |
Number of Layer |
Film Thicknesss / Layer |
% to SiO2 |
Number of Layer |
Hydrogen Concentration (%) |
HV |
(%) |
µk |
**20 |
BK7 |
7000 |
15 |
350 |
5 |
33 |
350 |
0 |
1700 |
60 |
0.20 |
21 |
3 |
1700 |
70 |
0.20 |
5 |
5 |
1700 |
77 |
0.17 |
22 |
10 |
1800 |
85 |
0.17 |
23 |
20 |
1800 |
90 |
0.17 |
"**" indicates a reference example. |
[0084] The followings can be understood from Table 1. When changing a film thickness of
the laminated film 102 by changing the number of repetitive lamination of both layers
while film thicknesses of each SiO
2 layer 104 and each SiC layer 106 being fixed, samples with thicker film thicknesses
(experimental examples 2 to 5) were confirmed to be usable comparing with samples
(experimental example 1) wherein a film thickness of the laminated film 102 was thin.
[0085] When changing a film thickness of the SiC layer 106 while keeping a film thickness
of the entire laminated film 102 and that of the SiO
2 layer 104 fixed, comparing with the samples (experimental examples 6, 9, 11, 14,
15 and 18), wherein a film thickness of a SiC layer 106 is out of a range of 30 to
60% of a film thickness of a SiO
2 layer 104, samples (experimental examples 7, 8, 12, 13, 16 and 17) within the range
were confirmed to be usable.
[0086] Even when thickening the film thickness of the entire laminated film 102 and keeping
the film thickness of each SiC layer 106 in a range of 30 to 60% of that of a SiO
2 layer 104, samples (experimental examples 10 and 19), wherein a film thickness of
one SiO
2 layer was out of the range of 5 to 30nm, were confirmed to be not as usable as samples
(experimental examples 8 and 17, etc.) within the range.
[0087] The followings can be understood from Table 2. When an amount of introducing hydrogen
to the region 60 (hydrogen concentration) increases when forming a SiC layer 106,
superior usability to that of the samples with no hydrogen introduced (experimental
example 20 and reference example) was confirmed.